Re: [PATCH v1] perf build: Don't compile demangle-cxx.cpp if not necessary

Ian Rogers
2023-04-27T05:27:59Z

On Mon, Apr 17, 2023 at 12:25 PM Ian Rogers <irogers@google.com> wrote:
>
> demangle-cxx.cpp requires a C++ compiler, but feature checks may fail
> because of the absence of this. Add a CONFIG_CXX_DEMANGLE so that the
> source isn't built if not supported. Copy libbfd and cplus demangle
> variants to a weak symbol-elf.c version so they aren't dependent on
> C++. These variants are only built with the build option
> BUILD_NONDISTRO=1.
>
> Signed-off-by: Ian Rogers <irogers@google.com>

Testing on arm and noticed we hadn't picked this one up.

Thanks,
Ian

> ---
> tools/perf/Makefile.config | 1 +
> tools/perf/util/Build | 2 +-
> tools/perf/util/symbol-elf.c | 27 +++++++++++++++++++++++++++
> 3 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 71442c54c25f..5f0f24b56f50 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -923,6 +923,7 @@ ifndef NO_DEMANGLE
> EXTLIBS += -lstdc++
> CFLAGS += -DHAVE_CXA_DEMANGLE_SUPPORT
> CXXFLAGS += -DHAVE_CXA_DEMANGLE_SUPPORT
> + $(call detected,CONFIG_CXX_DEMANGLE)
> endif
> ifdef BUILD_NONDISTRO
> ifeq ($(filter -liberty,$(EXTLIBS)),)
> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> index bd18fe5f2719..f9df1df1eec0 100644
> --- a/tools/perf/util/Build
> +++ b/tools/perf/util/Build
> @@ -214,7 +214,7 @@ perf-$(CONFIG_ZSTD) += zstd.o
>
> perf-$(CONFIG_LIBCAP) += cap.o
>
> -perf-y += demangle-cxx.o
> +perf-$(CONFIG_CXX_DEMANGLE) += demangle-cxx.o
> perf-y += demangle-ocaml.o
> perf-y += demangle-java.o
> perf-y += demangle-rust.o
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 35724f6a84fa..cd08bdb9824f 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -31,6 +31,13 @@
> #include <bfd.h>
> #endif
>
> +#if defined(HAVE_LIBBFD_SUPPORT) || defined(HAVE_CPLUS_DEMANGLE_SUPPORT)
> +#ifndef DMGL_PARAMS
> +#define DMGL_PARAMS (1 << 0) /* Include function args */
> +#define DMGL_ANSI (1 << 1) /* Include const, volatile, etc */
> +#endif
> +#endif
> +
> #ifndef EM_AARCH64
> #define EM_AARCH64 183 /* ARM 64 bit */
> #endif
> @@ -271,6 +278,26 @@ static bool want_demangle(bool is_kernel_sym)
> return is_kernel_sym ? symbol_conf.demangle_kernel : symbol_conf.demangle;
> }
>
> +/*
> + * Demangle C++ function signature, typically replaced by demangle-cxx.cpp
> + * version.
> + */
> +__weak char *cxx_demangle_sym(const char *str __maybe_unused, bool params __maybe_unused,
> + bool modifiers __maybe_unused)
> +{
> +#ifdef HAVE_LIBBFD_SUPPORT
> + int flags = (params ? DMGL_PARAMS : 0) | (modifiers ? DMGL_ANSI : 0);
> +
> + return bfd_demangle(NULL, str, flags);
> +#elif defined(HAVE_CPLUS_DEMANGLE_SUPPORT)
> + int flags = (params ? DMGL_PARAMS : 0) | (modifiers ? DMGL_ANSI : 0);
> +
> + return cplus_demangle(str, flags);
> +#else
> + return NULL;
> +#endif
> +}
> +
> static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
> {
> char *demangled = NULL;
> --
> 2.40.0.634.g4ca3ef3211-goog
>